An initial study into the deaths of hundreds of Peruvian seabirds, mostly pelicans and boobies, on the country’s northern beaches indicates they died of starvation due to a lack of their main food, anchovies.

The dead and dying seabirds have been littering beaches in Peru’s northern regions of Ancash, La Libertad, Lambayeque and Piura. More than 1,200 were found in one nature reserve and numbers are expected to reach several thousand and rising.

Scientists believe that a warming of Peru’s coastal waters, usually attributed to the El Niño phenomenon, has caused the shortage of Peruvian anchovies. The fish flourishes in the cold water Humboldt current, which hugs the Chilean and Peruvian coastline, and forms the base of a marine food chain which makes Peru’s Pacific waters one of the world’s biggest fisheries.

“Oceanographic changes may have affected food availability and there is a likelihood that this has affected the distribution of anchovies,” Patricia Majluf, a marine biologist and former fisheries ministers said.

“When there is a warming of sea surface temperatures the fish go deeper which means fledging juvenile pelicans, which cannot yet dive, are not able to feed themselves.” Majluf resigned on Friday saying the sector was “in disorder, full of irregularities and corruption.”

The majority of dead and dying birds found so far have been juveniles, many of them severely underweight. Peru’s health ministry has urged people to stay away from beaches where there are dead animals.

She added there was a “fairly high chance” of an El Niño event occurring later this year. The last major El Niño in 1997 and 1998 caused the deaths of millions of seabirds and other marine animals such as sealions.

The seabird deaths follow closely a massive dolphin die-off, which began in January, on the same stretch of coastline. The death toll could exceed 3,000, according to volunteers’ counts. It is among the largest ever reported worldwide.

The strandings are a mystery. Initially experts said the causes could be acoustic impact from testing for oil, now it seems more likely that the cause is a virus or other pathogen. However even in the US, the National Oceanographic and Atmospheric Administration (NOAA) classified more than half of recorded marine mammals strandings since 1991 as “undetermined”.

Raul Castillo, the scientific director of Peru’s Oceanic Institute said brucellosis and leptospirosis, both bacterial diseases, had been ruled out following port-mortem examinations on several dolphin carcasses.

However tests have yet to be completed for morbillivirus, a highly infectious virus related to measles in humans and canine distemper. The Florida-based Dolphin Research Centre says the morbillivirus has caused several cases of mass deaths among cetaceans in recent years.

“We know from studies in other countries that the dolphins most likely to get killed by viruses are those with the highest loads of contaminants in their bodies, like pesticides, herbicides and DDT,” said Stefan Austermuhle, a German zoologist specialising in Peru’s marine biodiversity who also heads Mundo Azul, an NGO.

He added the Peruvian authorities had handled the dolphin die-off extremely badly as many animals had been left to rot on the beach potentially exposing local residents to pathogens or contaminants. In some fishing villages, meat had been cut off the carcasses for food.